This invention relates to the field of lens systems, more particularly to lens systems used with micromirror based projection display systems.
Micromirror projection display systems are rapidly gaining acceptance in a wide variety of applications, from sub-three pound portable projectors to cinema-quality projectors. The cinema projectors provide the image quality of traditional film projectors, without the expense and degradation associated with filmstrip projection. Existing cinema projectors provide contrast ratios in excess of 1000:1. What is needed is a method of increasing the contrast ratio of micromirror projectors.
Objects and advantages will be obvious, and will in part appear hereinafter and will be accomplished by the present invention which provides a method and system for increasing the contrast ratio of a display system. One embodiment of the claimed invention provides a lens system. The lens system comprising: a first lens group on a light path; a second lens group on the light path; and an asymmetric aperture stop on the light path between the first and second groups.
Another embodiment of the present invention provides a display system. The display system comprising: a light source for providing a beam of light along an illumination path; a micromirror device on the illumination path for receiving the beam of light and selectively reflecting the beam of light along a projection path; a lens system on the projection path. The lens system comprises: at least one lens; and an asymmetric aperture stop receiving light from at least one of the lenses.
Yet another embodiment of the present invention provides a method of projecting an image. The method comprises: receiving an illumination light beam along an illumination path; selectively reflected the illumination light beam along a projection path in response to image data; focusing selectively reflected light using a projection lens; and blocking a portion of light passing through the projection lens using an asymmetric aperture.
According to one embodiment of the present invention, the asymmetric aperture stop is formed by adding a blocking region to an otherwise circular aperture. The blocking region is oriented towards the illumination path and away from a spectral reflection path. One embodiment uses a crescent shaped blocking region. The thickness of the crescent is 17% of the diameter of the aperture. The inside radius of the crescent is equal to the radius of the circular portion of the aperture. Alternative embodiment use blocking regions having other shapes.